How Do I Kill Algae Naturally?

How to kill pond algae naturally is a valid question, because most people usually associate the use of chemicals, namely algaecides, with killing algae. It’s our basic nature to want to simply kill something, get rid of it, and go on without more trouble. The only problem is, this approach doesn’t always work that well with ponds.

At the same time, many people are becoming aware that a more eco-friendly approach to home, garden, and pond care is a good thing and they want to know how to achieve a particular result without using the aformentioned chemical cocktails.

So when someone asked me the question, “how do I kill algae naturally?” I’ll normally tell them that you can’t. At least not directly.

Now I know that many folks will say, well, what about barley straw? What about beneficial bacteria? Plants?

All are good options to the degree that they all have a history of helping with an algae problem in some way. But it would be a mistake to say that any of them “kill” algae.
Products on the market like Algae Fix, Cutrine, EarthTec, and Algae Off are all chemical products that do actually kill algae. Some of these contain copper, which is toxic to algae, another will degrade the cell membrane, and another contains hydrogen peroxide, which when applied directly on the algae, will damage, and kill it. All of the above products are listed by the EPA as algaecides. The term “cide” as defined means “killing” or “killer”. In the same vein, herbicides may be use to control rooted aquatic plants.

Is Killing Algae The Best Option For Control?

My common answer to this question is no. Not everyone will agree with me on this aspect of pond management but it’s OK if they want to be wrong. Seriously though, common sense will dictate that you don’t want a bunch of dead plant matter building up at the bottom of your pond, but that’s just what happens when you kill algae off, intermittently throughout the season. Algaecides, you see, won’t help to break any of this dead material down, and if they contain copper, they’ll likely slow or restrict any natural decomposition that might take place.

I’m not going to stand here on an environmental soap box (you can find that elsewhere on this blog I suspect) and tell you that a chemical is never needed or useful in some situations. Sometimes they are. But I can also tell you that they are overused and abused due to ignorance, impatience, or savvy marketing from chemical companies.

I have long believed that algaecides will generally take a pond in the wrong direction where it’s health is concerned. They treat a visual symptom (algae) of a non-visable problem, (or in other words, high nutrient loads, heavy organic build up, depleted beneficial bacterial stores, or low dissolved oxygen levels in the water, must to name a few).

In the end, there are so many drawbacks to simply killing an algae bloom that in most cases, the negatives out-weigh the positives by a wide margin. This risk of fish loss, quickly repeating algae blooms, the possible increasing dependence on ongoing treatments are just a few undesirable side effects.

Pond Algae Can Be Managed Naturally

So instead of asking, how can I KILL algae, how about we make a shift in our thinking and look at ways we can manage a pond in such a way that will keep algae from being a problem.

It’s fine to use something like barley straw to keep algae from forming. Barley historically has always worked better as a deterrent, rather than a treatment of an existing bloom. I can’t tell you that people have never had algae go away, following a barley treatment but statistics show it’s best used before algae starts to get well underway. This likely applies to all forms of barley products, however most university studies used dried barley in their testing.

Beneficial bacteria though, has provided a natural way to restore a pond to a better condition, and in our testing and experience, it can help to create an environment where algae simply can’t grow well. The microbes can bind to various nutrients that algae would normally feed on, and as these nutrient sources drop become unavailable in abundance, then algae will slowly and gradually regress, often disappearing from the eye altogether.

Keep in mind here that we didn’t kill anything. We didn’t risk or harm anything, and we’re actually cleaning the pond up of organic loading, rather than the other way around. Now we can’t say that the beneficial bacteria killed or controlled the algae directly, the EPA won’t allow that by their current chemical regulations, however in my book, this is just fine. It doesn’t take away from the fact that thousands of ponds, in my personal experience, have been shifted into a cleaner and clearer condition by not killing anything at all.

Plants, and I’m using this example for small ponds primarily, will also work to sort of out-compete algae for nutrients and sunlight, and when their density is high enough to affect a change, algae will not prosper. Plants also provide protection from fish, and add a natural beauty to many “artificial” ponds, so I’m very high on plant use in most ponds and water gardens.
What About Other Pond Tools For Algae Control

Before we close out this discussion on how to kill algae naturally, it would be worth noting, I think, that mechanical options do exist that might allow a pond owner to avoid using chemicals in their ponds. I can’t categorize these things as “natural” but they can be effective. For small ponds with green water issues, do some research on UV light. Ultra violet light does actually kill or damage single cell algae fairly well, and when it’s used in combination with a good biofilter, many ponds will clear up quite well.

For large ponds, ultrasonic algae control may be a viable option to test. Ultrasound does damage and kill certain types of algae, in some cases up to 100% control, where in other situations, it may be much less efficient. Much depends on the algae types that are present in the pond and these should be evaluated to be sure that ultrasound is a good fit for your pond algae control requirements.

Hi Jackie…thanks for the question. Actually now that I look at it, that’s a typo…it should read “plants provide protection FOR fish”, simply because plants provide protective cover and concealment from predators, and to an extent if you have small fry, they’ll be more protected from other fish that might try to feed on them.

I have a small pond.1/2-1acre…. I have an algae problem that almost prevents me from fishing. I added grass carp two years ago, but have stayed away from chemicals so far. can you tell me specifically what you suggest I do?

Hi Albert…thanks for the question. I like carp but they may not always be enough to help with algae. My normal approach is to go at the problem with a combination of good aeration, meaning sub-surface aerating if it’s deeper than say six feet, and then use some kind of beneficial bacteria for several months to see if we can lower nutrients enough and clear the algae. When you reduce what feeds it, it will often regress quite a bit. For your size of pond, and I’m going to assume you’re maybe around 8′ deep let’s say, something like a 1/4 HP aerator with a single diffuser and a one acre biosphere pro would be what I would try. Treat with the spheres for 2 to 3 months but not longer if it isn’t really moving the needle. Often though it will help quite a lot. You can find both of these items on our online store at http://pondalgaesolutions.com